SYDNEY, Australia — President Bush flirted with the idea that American troop strength in Iraq could be reduced during a whirlwind visit to Anbar province on his way to an Asia-Pacific summit, where the war debate seemed sure to follow him.

Mr. Bush arrived here on a rainy Tuesday night after an unscheduled detour to the dusty war zone and the province that was once rife with insurgents. He arrived ahead of a summit of 21 Asia-Pacific countries.

The president told reporters aboard Air Force One on Monday night that his strategy sessions with American and Iraqi leaders and chats about morale with soldiers and Marines at an air base in western Iraq left him hopeful that positive change is starting in the 4-year-old conflict.

The question, he said, is, “Will it last?”

Mr. Bush is nearing a decision on how long to maintain the current American troop buildup. He sent 30,000 additional American troops to Iraq to enhance security in Baghdad and Anbar province. Despite military successes, political progress — especially at the national level — is lagging and Democrats and some prominent Republicans want troops called home.

“How many troops does it take to protect us?” Mr. Bush asked. “What does it take to have this Iraqi democracy succeed?”

Debate over the Iraq war was certain to surface at the Asia Pacific Economic Cooperation forum. Mr. Bush begins summit talks today, meeting with Prime Minister Howard of Australia, who joined with Mr. Bush and then- Prime Minister Blair of Britain in the invasion of Iraq. Mr. Howard is facing an aggressive election challenge from opposition leader. Kevin Rudd, and Mr. Rudd’s desire to pull Australian troops out of Iraq will surely be broached in the talks.

Mr. Bush also is scheduled to meet with leaders from Japan, China, Russia, and South Korea. Some have dubbed this year’s APEC the “China summit,” a reference to Beijing’s rising influence.

“Is this a China summit? The answer is absolutely not,” Mr. Bush said.

The presidential entourage had barely climbed aboard Air Force One, leaving dusty desert footprints on its blue carpet, when Mr. Bush invited reporters to a conference room for a 30-minute chat. He fiddled with a paper clip as he talked about his day at Al-Asad Air Base, a Saddam Hussein-era airfield now home to 10,000 American troops, who down bottle after bottle of water in sweltering 100-plus degree heat.

It was Mr. Bush’s third surprise trip to Iraq. The first two were to Baghdad.

This time he landed in the Iraqi desert, more than 100 miles west of the capital, to get on-the-ground briefings from advisers, including General David Petraeus, the top U.S.commander in Iraq, and Ryan Crocker, the U.S. ambassador to Iraq.

Mr. Crocker and General Petraeus are to testify before Congress next week. Their assessment of the conflict, along with a progress report the White House must give lawmakers by September 15, will determine the future course of the war.

“General Petraeus and Ambassador Crocker have said that if the security situation continues to improve the way it has, we may be able to achieve the same objectives with fewer troops,” Mr. Bush said.

He emphasized the word “if.” And he didn’t say how many troops could be withdrawn, or when.

Democratic presidential candidate Senator Biden, who planned to visit Iraq yesterday, said that if Mr. Bush was considering simply reducing troops below the pre-surge level of 130,000, “that’s not withdrawal.”

“The withdrawal would be getting us out of the middle of that civil war,” Mr. Biden said on CBS’s “The Early Show.” “There is virtually no political progress being made. … I hope everyone levels with the American people. This is a civil war and we shouldn’t be in the midst of it.”

Mr. Bush has refrained from thinking aloud about troop deployments. The president said security improvements in Anbar, where local sheiks have joined with U.S. forces against Al Qaeda, have given him confidence to “speculate on the hypothetical” — something he repeatedly refuses to do in answering reporters’ questions.

Mr. Bush said he quizzed the troops — who cheered him and Secretary of State Rice with shouts of “Hooh-rah!” — about morale. He said some soldiers and Marines complained that rotations were tough on their families, but added, “I wasn’t alarmed by what I heard.”

Asked if the discussions would affect his decision about troop levels, Mr. Bush turned resolute.

“The main factor that will affect my decision on troop levels is, can we succeed? What does it take to succeed?” Mr. Bush said, chopping the table with the side of his hand. “Because failure would lead to harm to America, is what I believe. As a matter of fact, I’m certain of it.”

The president described his meeting at the base with Prime Minister al-Maliki of Iraq as “comfortable.” He said the underlying question about the Iraqi government was: “Will this government go after killers?”